DETROIT (AP) -- A pioneering sex researcher's son who was cited for masturbating in New York's Central Park earlier this year was arrested in a rural Michigan sting operation for allegedly exposing himself to two female undercover investigators.

A completely nude William H. Masters III yelled for the attention of the two female kayakers on Saturday, then made obscene gestures from the bank of the Pinnebog River, Huron County Sheriff Kelly Hanson said.

The women were a sheriff's deputy and her assistant, who were taking part in a sting operation after a recent spate of similar incidents in the area.

Masters, the 60-year-old son of the late Dr. William H. Masters, who was one half of the famed sex research team of Masters and Johnson, was arrested with the help of a Michigan conservation officer.

Hanson said Wednesday that the sheriff's office has investigated four indecent exposure incidents in the area during the past two weeks, but added: "This has been going on for years."

The sheriff said "there are certainly similarities that we're looking into" between the case involving Masters and past incidents of indecent exposure in the Port Crescent State Park area, such as "this time of the year, that stretch of the river."

Masters, whose primary residence is in Southampton, N.Y., is charged with aggravated indecent exposure, a misdemeanor punishable by up to two years in jail and a $2,000 fine. He wasn't represented by an attorney during an initial court appearance on Tuesday. Neither he nor his wife returned phone messages from The Associated Press seeking comment.

Masters was arrested May 9 in New York City after a police officer reported seeing him expose his genitals and masturbate in Central Park. Court records show he was ordered to perform two days of community service under an agreement with prosecutors, who say the Michigan arrest might affect the New York case.

Masters' home in Michigan is in Pointe Aux Barques Township, which Hanson described as an older community where several wealthy families from around the U.S. own property.

Susan Gilbride, 54, of Grosse Pointe Park, said she was "totally blown away" by the news of Masters' arrest. The suburban Detroit resident said her family's Pointe Aux Barques summer home is a few doors down from one owned by Masters, whom she has known for more than 20 years and refers to as "Howie." Gilbride said she and her husband have dinner or drinks at least twice each summer with Masters and his wife, whom they still consider "close friends."

"He is an extremely warm, sensitive, compassion person," Gilbride told The Associated Press. "These are wonderful people ... This whole thing is just horrible. I can't imagine what they are going through right now."

Masters was freed on a $5,000 cash bond. His next court hearing will be on Sept. 13.

The elder Masters, who died in 2001, and his partner Virginia Johnson conducted interviews and observed sex in the act while researching the biological responses to sexual arousal. He and Johnson, whom he later married, wrote 1966's "Human Sexual Response," which was a best-seller.